1. Field of the Invention
This invention relates to electrical switches for controlling several electronic functions, especially functions of radio transceivers and, more directly, to an improvement in such switches to achieve both dual rate and bi-directional control of such a function over two conductors.
2. Prior Art
There are many prior art electrical switches for controlling multiple functions. A well known example is combination rotational off/on switch and volume control for a radio receiver. The demand for more complex electronic control functions in radio equipment requires more sophisticated switch control. Some known switches in related arts have cam surface actuators which interact with a plurality of individual electrical switches such that when the cam surfaces are repositioned in some manner, the individual switches are sequentially actuated. One principle difficulty with this arrangement is the size of the cam and switch combination and the number of interconnecting conductors which must be used between the location of the individual switches and the device which actually controls the function. The modern, very compact electronic radio transceivers, such as those for installation in automobiles, severly restrict the available for operator assessible switches. The front panels for this type of equipment tend to be very limited in size and the overall compactness of these designs frequently necessitates relocation of the devices for controlling functions to positions remote from the front panel. The compact space allocations do not always provide space for the inclusion of multiple conductor cables running between a power source, a front panel switch location and the device controlling the function. Thus it is advantageous to have both small actuator size and a minimum number of conductors running between the switch actuator location and the location of the controlling device.
Another type of known bi-directional switch, a quadrature switch, has been used in prior art radios which have frequency synthesized tuning systems. The quadrature switch is designed to simulate, by digital encoding, the operation of a standard rotating mechanical tuning knob. A shaft actuates a pair of followers which are connected to two separate series of detent positions arranged to be slightly out of phase. This combination produces high and low signal pulses corresponding to the separate followers contacting each level of the detents when the shaft is rotated. For rotation in either direction, signals will be recieved from one of the followers before signals are received from the other. It is this initial sequencing which determines the direction of rotation and, correspondingly,the direction of tuning change. The speed of tuning is determined by the rate at which the regularly spaced detent positions are contacted by the followers. This rate is digitally decoded and supplied to a control device to determine the speed of tuning adjustment. While the quadrature switch most closely simulates the operation of the well known mechanically actuated dial tuning device, it, too requires considerable space on or very near the front panel of the radio and a plurality of electrical interconnections to a frequency control device.